1. Field of the Invention
The present invention relates to a vibration wave motor, and more particularly to a structure of a vibration wave motor driven by a travelling vibration wave.
2. Related Background Art
A vibration wave motor utilizes a reciprocal motion generated when a periodic voltage is applied to a piezoelectric vibration element, as a drive force. It has an advantage over a conventional electromagnetic motor in that it is simple and compact in structure because windings are unnecessary and has high torque at a low rotation speed. In such a vibration wave motor, displacement of a vibration member is transmitted to a movable member by a method disclosed in Japanese Patent Application Laid-Open Nos. 178988/1984 and 201685/1984.
FIG. 1 shows the structure of such a prior art vibration wave motor and FIG. 2 illustrates a principle of operation. Numeral 1 denotes piezoelectric elements which function as electro-mechanical transducers, numeral 2 denotes an elastic member which functions as a vibration member, numeral 3 denotes a movable member, numeral 4 denotes a supporting vibration absorber and numeral 5 denotes a base element. The piezoelectric elements 1 are polarized across their thickness in sector areas shown by broken lines as shown by (+) and (-) in a plan view in FIG. 3.
An A.C. voltage V=V.sub.0 sin Wt is applied from a voltage source (not shown) to the piezoelectric elements (1a for a phase A, and a voltage V=.+-.V.sub.0 cos Wt is applied to the piezoelectric elements 1b for a phase B which are deviated by .lambda./4 to generate a travelling bending surface wave (or travelling vibration wave) in the elastic member 2 which is in contact with the piezoelectric elements 1. Thus, the movable member 3, in contact with the elastic member 2 is moved in either direction A or oppositely thereto.
The elastic member 2 has projections 2A for amplifying an amplitude of the travelling bending surface wave. The amplification factor of the amplitude is determined by a length l of the projection 2A (see FIG. 1).
The movable member 3 is in contact with the elastic member 2 under pressure and is moved at a velocity u by a friction force to the elastic member 2. The vibration member comprising the piezoelectric elements 1 and the elastic member 2 is supported by the vibration absorber 4 such as belt so that it does not propagate vibration to the base member 5.
In the vibration wave motor constructed as described above, the elastic member 2 is made of duralumin or brass having a low internal loss of vibration, and the projections 2A are cut from the elastic member 2 by a milling cutter or a wire cutting electric spark machine. However, such methods require a long time and a high cost.